1. Field of the Invention
This invention relates to a pseudo telephoto camera which makes it possible to take pictures in a "trimming mode" in which information on a selected portion of the field of view of an objective to be printed on a printing paper by enlarging printing is recorded on a negative onto which the whole field of view of the objective lens is projected, so that the information can be used for the enlarging printing, and more particularly it relates to a rear conversion lens system used for converting the focal length of the picture taking optical system of the camera into a longer value.
2. Description of the Prior Art
A pseudo telephoto camera of the above mentioned type has been proposed in Japanese Patent application laid-open number Sho. No. 54-26721. Upon printing, the selected portion of the field of view on the negative is printed on a printing paper at a magnification determined by the information recorded on the negative, so that the resulting print has an image size which is the same as that of a print obtained by printing of a negative produced by a normal photographing using an objective lens whose focal length equals to the pseudo focal length of the camera. Here the greater the printing magnification is, in other words, the smaller the selected portion of the field of view is, the longer the pseudo focal length is and the greater the magnification of the printed image is.
But, when the printing magnification becomes greater, graininess of a printed photo becomes outstanding, so that the upper limit of the printing magnification is limited. This maximum magnification is determined by considering, together with the observer's capability of perception, a brightness condition of a main object, exposure factors such as an aperture value, and characteristics of a film and a printing paper. Assuming that a print of a normal size (8 cm.times.12 cm) is made of a negative produced with these conditions being ordinary ones, the maximum printing magnification is approximately three to four times as great as in the case of a normal printing in terms of focal length of the objective lens.